.Gums, Resins, 



200 



[April 1907. 



the heavy metals also produce agglutination, but with weaker solutions 

 than is necessary with the salts of the alkaline earth. Hydrochloric, nitric and 

 acetic acids all cause agglutination ; very dilute sulphuric acid also has the same 

 effect, but if more concentrated coagulation commences. Trichloracetic acid, even 

 when very dilute, produces a remarkably elastic coagulum. Acetone also is a 

 coagulant. 



Regarding the action of mixtures, as a rule alcohol added after a salt 

 produces agglutination or coagulation. With solutions of the salts of monovalent 

 metals only agglutination occurs, and then the solutions must be very strong. 

 Salts of bivalent metals on the other hand, even in very weak solutions, induce good 

 coagulation. By gradually reducing the quantity of alcohol, coagulation gives place 

 to agglutination, and with still less alcohol there is no reaction. It is therefore 

 evident that the former is an intensification of the latter, since both are caused by 

 the same agent; it is only a matter of concentration. Acids in conjunction with 

 alcohol act like the salts of bivalent metals, but alkalies give no result. On studying 

 the influence of alkalies on the coagulation of the latex it was found that an 

 extremely small quantity interfered with the reaction ; a ten-thousandth normal 

 solution was sufficient to prevent agglutination or transform coagulation into agglu- 

 tination. Thus magnesium chloride and alcohol produce coagulation, but if the 

 latex is rendered even very slightly alkaline, only isolated flakes are formed, again 

 showing that the passage from agglutination to coagulation is gradual, and that 

 one may be considered as a higher stage of the other. 



Conclusions of practical importance to be drawn from these investigations 

 are that having now discovered that our knowledge of colloids is applicable to the 

 coagula tion of the latex of caoutchouc, we have every right to regard the latex 

 in the same light as an emulsion. 



Emulsions or colloidal solutions are charged electrically, either positively 

 or negatively. It is essential to know which, since their precipitation is regulated 

 thereby. The dialysed latex of rubber was found to be negatively charged. 

 Accordingly, as negative emulsions are precipitated by acids and by salts of bi- 

 and trivalent metals, and positively charged emulsions by alkalies and by salts of 

 bi- and tribasic acids, it is readily understood why salts of monometals act differently 

 to those, bivalent metals, and why acids react and alkalies do not, since the caout- 

 chouc latex only confirms the general law, further establishing the connection 

 between the properties of colloidal solutions and those of the rubber latex. — India 

 Rubber Journal. 



IMPORTS OF GUTTA PERCHA. 



The imports of gutta percha, which had been steadily declining since 1900, 

 till in 1904, when the amount was only one-fifth of Avhat it was in the former year, 

 again showed a rise, nearly double the amount of crude gutta coming into this 

 country, but of this about one-fifth was re-exported. 



Gutta percha is largely produced in British Possessions 5-9ths of our imports 

 coming therefrom, while Venezuela contributes 3-9ths, the remainder coming from 

 the Continent, whence it is imported in a partly-worked condition, and is entered as 

 raw material.—/. R. Journal. 



